1. Technical Field
The invention concerns an injection molding unit for a plastics injection molding machine for processing plastifiable materials such as synthetic materials, powdery and ceramic masses of the type including a carrier block; a receiving body fixable at the carrier block and adapted for receiving a feeding means penetrating the carrier block for feeding the plastifiable masses into a mold cavity of a mold; an injection bridge at which the feeding means is seated and which is displaceable towards and away from the carrier block for movement of the feeding means relative to the receiving body; a plurality of spindle drives each having a spindle and a nut as parts movable one against the other, wherein one of the movable parts is seated at the carrier block and the other at the injection bridge; and an injection motor movable together with the carrier block for driving one of the movable parts of the spindle drives at the carrier block.
2. Prior Art
Such an injection molding unit is known from EP-B 427 866. It refers to a two-plate-system comprising a carrier block as a front plate and an injection bridge as a back plate. The plasticizing cylinder is fixed at the carrier block. A feed screw penetrates the carrier block and is rotatably mounted at the injection bridge. The dosing motor is driven via a dosing motor arranged on the injection bridge and projecting in the direction towards the carrier block into the space between the carrier block and the injection bridge. In the same way the injection motor is arranged in the vertical projection between carrier block and injection bridge and drives via a belt drive two spindle drives, which when actuated, move the injection bridge towards and away from the carrier block. This movement at the same time generates the axial movement of the feed screw. The injection motor, however, is arranged so that its overall length determines the minimum distance between carrier block and injection bridge. Since the more the torque increases, basically the overall length of the injection motor increases, and by this construction natural limits are set to a compact design. A drive unit for moving the plasticizing cylinder towards the mold is not integrated in the injection molding unit.
From EP-A 576 925 an injection molding unit is known, wherein a carrier block is seated via spars at the stationary mold carrier. A drive unit formed as a hollow shaft motor for attachment of the nozzles to the injection mold and an injection unit, which generates the axial movement of the feed screw within the plasticizing cylinder during injection, are serially connected at the spars. The rotational motor for the rotation of the feed screw is provided at an injection bridge. This solution certainly makes possible a reliable symmetrical force introduction of the forces generated by the drive unit and the injection unit, however, the serial arrangement of these two units as well as the arrangement of the rotational motor in the direction towards the injection axis results in a large overall length of the injection molding unit, leading to a corresponding enlargement of the whole injection molding machine.
A two-plate-system is also known from DE-C 43 17 998, wherein, however, the drive unit for attachment of the nozzle to the injection mold is integrated into the injection unit. Electromotors serve as drives, which drive the hollow shafts of the drive unit and injection unit which are nested into one another. By this, a space-saving construction is obtained, however, due to the arrangement of the rotational motor at the very back end of the injection bridge an imbalance is produced, since by the nesting of drive unit and injection unit the rotational motor has no counterweight at the injection molding unit. Besides, belt drives have proved to be of short life, susceptible to damage and unprecise.